EMS Registry Ready

Sinus rhythm with an aberrantly conducted PAC on an ECG strip

An early P wave followed by a wide QRS: a PAC conducted with a bundle branch block.

What to look for

The PAC comes early enough to reach the bundle branches before the right one has recovered, so its QRS is wide (usually a right bundle branch block shape). How do you tell it from a PVC? Look for the early P wave in front of it, and check the T wave before, because that's often where the P is hiding.

Examples

Each strip is 6 seconds of lead II, drawn to scale (25 mm a second, 10 mm a millivolt), so you can count boxes the way you would on paper. Each one is a different example, measured below it.

Example 1 · lead II · 6 seconds
II25 mm/s · 10 mm/mV
Rate
90/min underlyingThe whole strip averages 93/min · 9 QRS complexes in 6 seconds × 10 = 90/min
Rhythm
Regular underneath, with early beats breaking it
P waves
Sinus P waves, plus early P waves of a different shape (the PACs)
P to QRS
1:1; each PAC's early P is followed by its own QRS
PR
0.18 s
QRS
0.08 s, narrow
PACs
2 on this strip
Example 2 · lead II · 6 seconds
II25 mm/s · 10 mm/mV
Rate
89/min underlyingThe whole strip averages 95/min · 9 QRS complexes in 6 seconds × 10 = 90/min
Rhythm
Regular underneath, with early beats breaking it
P waves
Sinus P waves, plus early P waves of a different shape (the PACs)
P to QRS
1:1; each PAC's early P is followed by its own QRS
PR
0.18 s
QRS
0.07 s, narrow
PACs
2 on this strip
Example 3 · lead II · 6 seconds
II25 mm/s · 10 mm/mV
Rate
73/min underlyingThe whole strip averages 80/min · 7 QRS complexes in 6 seconds × 10 = 70/min
Rhythm
Regular underneath, with early beats breaking it
P waves
Sinus P waves, plus early P waves of a different shape (the PACs)
P to QRS
1:1; each PAC's early P is followed by its own QRS
PR
0.13 s
QRS
0.08 s, narrow
PACs
2 on this strip

Don't confuse it with

Want a new strip every time? The ECG Drill in the app draws a fresh, measured example on every try and steers you toward the rhythms you miss. It's part of the Paramedic level, and you can try 5 strips a day free.

Try the ECG Drill

Where the criteria come from

Others in the Atrial group